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41.
An investigation of the natural products chemistry of the red alga Delisea pulchra, collected from the Cape Banks, New South Wales, Australia, yielded eight new polyhalogenated furanones (1–7) and the previously reported metabolites 8–24). The structures of 1–8 were determined from the interpretation of their 1D and 2D NMR, UV, IR and mass spectral data. For the first time, complete 1H and 13C NMR data for compounds 14, 18, and 20-23 are reported. 相似文献
42.
Baldelli E Battaglia A Bombardelli E Carenzi G Fontana G Gelmi ML Guerrini A Pocar D 《The Journal of organic chemistry》2004,69(20):6610-6616
New taxanes 15 and 18, containing the unsaturated and saturated baccatin[14,1-d]furan-2-one nucleus, respectively, were prepared starting from the readily available 13-oxo-7-Tes-baccatin III (3). Sequential formation of the enolate of 3 and reaction with ethyl glyoxylate gave the 13-oxo-7-Tes-baccatin[14,1-d]-3,4-dehydrofuran-2-one 4. The reduction of 4 can result in the formation of a mixture of compounds corresponding to 13-hydroxy alcohol 5 and 13-enol derivative 6. Both 5 and 6 were transformed into 13-oxo-7-Tes-baccatin[14,1-d]furan-2-one 8 by treatment with a base. Further reduction of 8 gave 13-hydroxy compound 9. Esterification of 6 and 9 with N,O-protected norstatine 12, followed by deprotection, gave the new promising anticancer taxanes 15 and 18, respectively. 相似文献
43.
The P-type delayed fluorescence (DF) Si→So of aromatic compounds results from the population of excited singlet states Si by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T1 : T1 + T1 Si + So; Si may be any excited singlet state whose excitation energy E(Si ? 2 E(T1). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(TA1) < E(T1B), hetero-TTA may lead to excited singlet states SkA which are not accessible by TTA of 2 T1A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state SkA which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h10 or anthracene-d10 or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. SkA is the lowest 1B3U+ state (Bb state) of anthracene. 相似文献
44.
Tiberiu-M. Gianga Edwige Audibert Anamaria Trandafir Gabriele Kociok-Khn G. Dan Panto 《Chemical science》2020,11(35):9685
We report herein the first all-donor aromatic [2]catenane formed through dynamic combinatorial chemistry, using single component libraries. The building block is a benzo[1,2-b:4,5-b′]dithiophene derivative, a π-donor molecule, with cysteine appendages that allow for disulfide exchange. The hydrophobic effect plays an essential role in the formation of the all-donor [2]catenane. The design of the building block allows the formation of a quasi-fused pentacyclic core, which enhances the stacking interactions between the cores. The [2]catenane has chiro-optical and fluorescent properties, being also the first known DCC-disulphide-based interlocked molecule to be fluorescent.An all-donor [2]catenane has been synthesised via dynamic combinatorial chemistry. It features stacked benzodithiophenes which are quasi-pentacyclic through hydrogen bonding. 相似文献
45.
A simple model is proposed to describe flocculation of fine particles by high polymers. The model is based on the assumption that the number of colloid particles attached to a single polymer molecule is a random quantity, and that a minimum number of particles must be attached to a polymer molecule to trigger its removal from the system. The predictions of the model are confronted with experimental data concerning the stability of the system polyacrylamide-sol AgJ. 相似文献
46.
Stepan S. Basok Gabriele Bocelli Eduard V. Ganin Marina S. Fonari Yurii A. Simonov 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(1):o50-o52
In the title compound, 2C8H18NO3+·2C7H6NO2−·3H2O, proton transfer occurs from the carboxylic acid group of the 4‐aminobenzoic acid (PABA) molecule to the amine group of the macrocycle, resulting in the formation of a salt‐like adduct. The anions are combined into helical chains which are further bound by the water molecules into sheets. The macrocyclic cations are situated between these layers and are bound to the anions both directly and via bridging water molecules. The structure exhibits a diverse system of hydrogen bonding. 相似文献
47.
Arturo Battaglia Eleonora Baldelli Gabriele Fontana Andrea Guerrini 《Tetrahedron》2005,61(32):7727-7745
The base induced deprotonation of H-14 of 7-triethylsilyl- (7-TES-) and 7-tert-butoxycarbonyl- (7-BOC-) protected 13-oxo-baccatins gave the corresponding enolates, which were selectively aminated with electrophilic nitrogen donors, such as azodicarboxylates and tosyl azide. In particular, tosyl azide gave the corresponding 7-BOC- and 7-TES-13-oxo-14β-azido-baccatin III. Alternatively, the last compound was prepared via NaN3 induced azidation of the 13-silyl enol ether of 7-TES-13-oxo-baccatin III under oxidative (cerium ammonium nitrate) conditions. The 13-silyl enol ether was obtained in a multistep process by DBU induced silylation of 7-TES-13-oxo-baccatin III. The 7-TES-13-oxo-14β-azido-baccatin III was used as a key intermediate for the synthesis of a new family of antitumour taxanes containing amino based functional groups at the C-14 position, such as: 14β-azido, 14β-amino, 14β-amino 1, 14-carbamate, 14β-amino 1, 14-thiocarbamate, and 14β-amino N-tert-butoxycarbonyl-1,14-carbamate. 相似文献
48.
Bezhan Chankvetadze Gabriele Endresz Gottfried Blaschke 《Journal of chromatography. A》1995,700(1-2):43-49
Enantiomeric resolutions of some chiral pharmaceuticals containing the imidazole (1,3-diazole) moiety were carried out using capillary electrophoresis. Various native cyclodextrins (ga-, β- and γ-cyclodextrin) and derivatized cyclodextrins (hydroxypropyl-, and sulfobutyl ether-β-cyclodextrin) were used as chiral buffer modifiers. The effects of the cavity size, the structure and the charge of the selectors on the chiral recognition ability were evaluated. The influence of the type and concentration of the organic modifier on the separation of miconazole enantiomers and the pH of the run buffer on the separation of enilconazole enantiomers was also studied. 相似文献
49.
The simulation of charged and/or strongly polar solutes represents a challenge for standard molecular-dynamics techniques. The use of periodic boundary conditions (PBCs) leads to artifacts due to the interaction between two replicas in the presence of the long-range Coulomb forces. A way to avoid these problems is the use of nonperiodic boundary conditions. A possible realization is to consider a finite system, a sphere, embedded in a reaction field described by the method of the images. In the present work the modified image approximation has been implemented in a molecular-dynamics code and optimized for the use of two standard solvents, water and acetonitrile. The methodology has then been applied to investigate the conformational changes in water-solvated alanine dipeptide. The free-energy surface calculated with this method is comparable to that obtained with PBC. 相似文献
50.
Andr Müller Walter Keller-Schierlein Jacek Bielecki Gabriele Rak Joachim Stümpfel Hans Zhner 《Helvetica chimica acta》1986,69(8):1829-1832
(2S, 3R, 4R, 6R)-2,3,4-Trihydroxy-6-methylcyclohexanone from Two Strains of Actinomycetes A tetrazolium-blue positive compound was isolated from two strains of acinomycetes. Its constitution and relative configuration 1 were determined by spectroscopic methods, and the absolute configuration by degradation to (+)-(R)-methylsuccinic acid. 相似文献